[Images] Reconstructions of Ammonoids and Nautiloids

Colossal Squid

Please find to follow a series of artistic reconstructions of important and varied nautiloid, ammonoid and ammonite genera. The images were obtained from this Japanese website but the brief descriptive text I have compiled from a number of varied sources. These images are simply too excellent not to use in this context.

I have placed the species in approximate chronological order and provided dates where possible. Those forms that I have provided a single date for rather than a range of dates does not mean that that species was very short-lived, but rather I have been unable to establish a date range, I will update this as and when I can.

Please note that the soft-bodied animal depicted in the drawings is by no means definitive and is conjectural, (e.g. number of arms, colour, presence of a hood etc) but they do provide an excellent suggestion of what these ancient shelled cephalopods may have looked like.

(Given my absolute lack of Japanese language ability and an appropriate keyboard, if any kind TONMO volunteer would like to notify the Japanese webmaster of this thread I would be most greatful. Also, I have made this thread sticky as it would be a pity for it to disappear down the forum as it has taken many hours to compile. In addition, I have locked it so that we can keep it to purely a list of species and descriptions. That way we can add more at a future date without sandwiching them between discussion threads.)

If anyone would like to discuss any of the fossil cephalopods listed, please do so in this thread:

The first ancient cephalopod in our list is represented by this depiction of the giant nautiloid Endoceras. The shell of Endoceras is absolutely typical of the orthoconic nautiloids and consists of a characteristic long conical shell composed of a series of interlinked cones (endocones) connected with a sub-ventral siphuncle. Due to the size and fragility of the shell, complete large fossils are unknown, but fragments are commonly found that have been projected to huge sizes. Endoceras probably reached at least 3.5m in length, but some other members of the Endoceratidae (e.g Cameroceras see below) may have reached much larger sizes. Such a shell shape allowed Endoceras to cut through the water at great speed as it would have minimised drag, though it may have not been especially manouverable. It represents the top predator of its time, and probably fed on trilobites and other small shelly creatures. It had a worldwide distribution, but is mostly known from North America and Sweden, deposits of this fossil are known as ‘Orthoceras Limestone’ and often used for a resilient flooring material. The Endoceratida were the first of the nautiloid orders to go extinct.

A close relative of Endoceras, this gigantic cephalopod is certainly one of the very largest cephalopods that has ever existed. It's shell is thought to have reached up to 11m in length. The top predator of it's time, Cameroceras failed to survive the Middle Ordovician. Due to it's immense bulk, Cameroceras is not thought to have been a very fast or manoeverable swimmer, and it probably drifted over the sea floor rooting out sea scorpions and tribolites with its arms. Fossils are restricted to North America and Europe.

Colossal Squid

Orthoceras is a typical nautiloid of this early period. The shell is shaped like a tapering cone and is made of many chambers joined together by a centrally placed tube known as a siphuncle. This shell form is known as ‘orthocone’. Orthoceras was an active hunter and predator, probably swimming with its shell held horizontally weighted down by mineralised deposits within the shell. Typical Orthoceras reached 15cm in length though some closely related species reached giant proportions. Fossils of this animal are mainly found in Europe. The artist has reconstructed Orthoceras with a head very similar to the modern Nautilus, but we really do not know if this was the case or not as no soft-bodied nautiloid fossils of this period have been found.

Another early nautiloid, Cyrtoceras had a hook shaped shell known as ‘cyrtocone’. The chambers in the shell were closely spaced but the animal lived in a long living chamber. Experiments using models have demonstrated that Cyrtoceras probably swum along head-down in the water and probably scavenged close to the sea-bed. Found world-wide, a typical Cyrtoceras measures 12cm in length.

Despite its similar appearance, Estonioceras is not believed to be ancestral to the ammonoids but is thought to have developed a similar shape due to a similar lifestyle. This rare fossil nautiloid is very loosely coiled with the final whorl containing the living chamber growing away from the shell. Unusually for nautiloids, the siphuncle is placed near the outside of the whorl, most nautilod siphuncles are centrally placed. It is thought to have lived in a swimming lifestyle in possibly fairly deep water. Known from Estonia and other parts of Europe, Estonioceras grew up to 10cm in diameter.

Colossal Squid

Clymenia is an extremely primitive ammonoid and can be regarded as a short-lived experiment amongst the cephalopods. It is part of a small group of ammonoids though its fossils are not uncommon in Late Devonian rocks. It is very smooth, flat and disc-shaped with simple sutures. In these Clymeniida, the siphuncle, or tube that connects the shell chambers to the head, is located close to the outer side of the spiral (dorsal), whereas the later ammonoids had theirs in the inner side (ventral). The Order Clymeniida is not thought to have survived the Late Devonian and is not believed to have given rise to any of the later ammonoid groups. Clymenia measures about 4cm in diameter and is restricted to Europe, North Africa and possibly Australia. It probably adapted to a predatory role high in the water column.

Another member of the Clymeniida, this bizarre and extremely rare ammonoid had a triangular form. The distribution is the same as of Clymenia above but the animal was smaller, typically just 2cm across. Although it is believed to have been capable of swimming, the animal probably spent much of its time on the sea bed possibly lying flat.

Please click here to access a 2005 research paper describing new specimens of Soliclymenia from Poland.

Goniatites (ammonoid)

Early Carboniferous (342-323mya)

Order: Goniatitida
Family: Goniatitidae

Goniatites is a very early ammonoid and is quite primitive with simple suture lines dividing the chambers; it can be interpreted as an early ancestor of the true ammonites. Goniatites is a variable form with various species broad, disc-shaped or almost round in form. The smooth but poorly streamlined form suggests that it was a unremarkable swimmer in the Carboniferous shelf-seas and it probably lived in swarms off-shore over reefs. Some forms of goniatite have a notch in the shell where the siphon would protruded and the more complex suture lines of later species indicates that in some cases they were able to live in relatively deep water. Goniatites is found all over the world and generally grew up to 6cm in diameter.

For more information on Goniatites click here. A downloadable goniatite database is available on a zip file at the following site: Goniat

Colossal Squid

Ceratites are seen as a mid point between the goniatites and the ammonites with a suture pattern that is more complex than goniatites and less complex than the ammonites. They were by far the most important cephalopod during the Triassic and underwent a great radiation with many differing forms evolving, some with very complex sutures. They are mostly found in Triassic limestones indicating they had a preference for warm shallow continental seas. None survived into the Jurassic period and they were replaced by the ascendant true ammonites which had evolved from the ceratites. Found all over the world, Ceratites grew up to 6cm in diameter.

Click here for an excellent ceratite fossil displaying the suture pattern in detail.

Echioceras (true ammonite)

Early Jurassic (200-180mya)

Order: Ammonitida
Family: Echioceratidae

An early ammonite, the heavily ribbed Echioceras is thought to have dwelled in shallow shelf seas. From the shape of the shell, it appears that it would not have been a fast swimming ammonite and was probably either a scavenger or caught slow moving prey. It is found worldwide and has a typical diameter of 6cm.

Click here for specimen of Echioceras found at Charmouth in Dorset, UK.

Oxynoticeras (true ammonite)

Early Jurassic (201-195mya)

Order: Ammonitida
Family: Oxynoticeratidae

Found worldwide, this extremely thin ammonite would have been an efficient swimmer, being so streamlined. The knife-edge of the shell would have offered minimal resistance to the water and it is thought this one of the fastest swimming ammonites of them all. It typically has a diameter of 10cm.

Here is a nice specimen of Oxynoticeras also from Charmouth in the UK.

Colossal Squid

This is a reconstruction of Belemnotheuthis (aka Belemnoteuthis = Acanthoteuthis) based on the remarkably preserved type specimen also shown below. Belemnotheutis was a coleoid cephalopod, akin to squid, octopus and cuttlefish, unlike the externally shelled cephalopods shown above. It is known from fossils discovered in the Arctic and from Europe, especially in the German Solnhofen deposits. The particular specimen shown below was recovered from the Oxford Clays at Christian Malford in England where many remarkably preserved fossil squid have been recovered with phosphatised soft parts. The coleoids from this site were recovered during the construction of a railway line in 1840.

Belemnotheutis was not a belemnite but probably represents a sister group; the precise relationship of this animal to that group remains unresolved. The body grew to approximately 25cm and it was equipped with an ink-sac. It had ten equally lengthed arms equipped with both suckers and hooks attached to a small head whilst the body contained a broad conical phragmocone and a short rostrum, tapering to a thin aragonitic sheath. It probably formed a major dietry component of many marine reptiles, but was itself an effective predator capable of powerful swimming.

Desmond Donovan and MD Crane's 1992 paper on Belemnotheutis can be found here. Aside from an anatomical description, this paper details the feud that developed between Richard Owen, Joseph Pierce and Gideon Mantell in attempting to classify the specimen.

Kosmoceras (true ammonite)

Mid Jurassic (164-159mya)

Order: Ammonitida
Family: Kosmoceratidae

Kosmoceras is particularly interesting as it displays extreme dimorphism between the two sexes. The drawing depicted is of the microconch, almost certainly the male, which has two very large extensions to the shell either side of the aperture, these are known as lappets. The larger female Kosmoceras ammonite, known as the macroconch, did not have these structures and was somewhat smoother in appearance. It is generally believed that the male used these lappets as a form of display in order to attract a mate and is quite possible that these lappets were brightly coloured. In addition, the microconch also developed short spines on its shell, another feature lacking with the smooth female. The implication is that at least some forms of ammonite had highly developed eyes and were clearly very visual animals. Kosmoceras is known mainly from Europe and grew to about 6cm in diameter.

This late Jurassic ammonite is known from Russia, northern Europe and Greenland. It is one member of a very successful ammonite group characterised by its heavy branching ribs on its shell. It typically measures 4cm in diameter, though some species grew up to 10cm.

Found worldwide, this peculiar ammonite has a very loose coiling so that the whorls are not in contact, this arrangement developed many times amongst the nautiloids and ammonoids. This ammonite is thought to have been adapted to a predatory lifestyle in moderately deep shelf seas. The extremely rare Crioceratites spinosus has delicate spines and only a handful of these have ever been found, a typical diameter measures about 10cm.

Colossal Squid

Scaphites is another peculiar heteromorph ammonite. It is known from all over the world but is particularly common in the Western Interior Seaway in North America; from the stomachs of plesiosaurs excavated there we know it was probably a major dietary component of these marine reptiles. The animal initially developed the familiar whorl shape, later developing a short shaft and a hook-shaped terminal living chamber. This short broad scoop-shaped living chamber somewhat resembles a Nautilus in shape and is unlike most other ammonites, which usually had long and narrow living chambers. They were adapted for life on the sea-floor and some researchers have speculated that they may have had a similar lifestyle to Nautilus. It grew up to 20cm in length.

A typical late Cretaceous ammonite, these small ammonites were extremely variable in appearance, hence the genus and species name Schloenbachia varians. Some were quite smooth and flat, but others such as the example here were covered in tubercles and spine-bases. Schloenbachia was thought to be a good swimmer and grew to a moderate size of 25cm. The descendants of this ammonite, such as Euhoplites, were the most ornamented forms to evolve. Finds are most common from Europe and Greenland.

The most bizarre ammonite to evolve, Nipponites appears at first glance to be an irregular tangle of whorls, but is actually quite regular in construction. Each bend in the shell is a U-bend twisting in the X, Y and Z axis, so that the mature animal would have resembled a globular coil. It probably evolved from an animal somewhat akin to Bostrychoceras, noted below, and probably shared a similar lifestyle, drifting in the open water with its arms sweeping for plankton. It is doubtful if it had any swimming ability at all. Nipponites is known from Japan and Kamchatka; a typical specimen measures 6cm in diameter.

Here is a specimen recovered by a Russian-Japanese expedition in 1999.

Colossal Squid

This Late Cretaceous ammonite grew to a considerable size, up to 50cm. This ammonite had a very thick smooth shell and was highly compressed, indicating that it was probably an extremely fast-moving ammonite. Examples recovered from the Western Interior Seaway of the US have displayed bite-marks from large marine lizards. It is found worldwide.

Here is an excellent specimen of Placenticeras, whilst here is a reconstruction of the animal that can be seen at the Savage Ancient Seas travelling exhibition.

Pachydiscus (true ammonite)

Late Cretaceous (84-65mya).

Order: Ammonitida
Family: Pachydiscidae

One of latest species of ammonite to evolve, the Pachydiscidae included some of the largest forms with some species approaching 2m in diameter. With a mildly compressed shell and gently curving ribs, Pachydiscus is thought to have been a competent swimmer in an open sea environment. It has an extremely complex suture pattern and has a worldwide distribution with the largest specimens found in Canada.

This is a reconstruction of the largest ammonite found to date. Hailing from Munster in Germany, Parapuzosia seppenradensis measures a gigantic 2.2m across, and even at this size it lacks the living chamber! The entire fully grown animal may have measured in excess of 2.5m. Probably an unremarkable swimmer, this ammonite probably hunted or scavenged on the seabed.

A full size reconstructed version of this huge animal can be seen here, please click on the thumbnail images.

A truly bizarre heteromorphic ammonite, this is a fairly common fossil from Hokkaido in Japan, but is rare elsewhere. This small ammonite must have toppled as it grew due to the shifting orientation of the shell. It has been speculated that this animal lived a benthic life at moderate depths and probably sought shelter on the sea bed. It grew up to about 200mm in length.

Bostrychoceras developed helical coiling much like that of a snail or gastropod in
contrast to the flat coiling of most ammonites. This coiling is very loose so that the coils are not in contact with each other. The living chamber is U-shaped, and the aperture was directed forward in life, so that the protruding arms would not have been in contact with the sea bed below. Palaeontologists believe that this genus was probably planktonic, floating in the open ocean and feeding on small animals in the water column whilst slowly rotating and sweeping the currents with its delicate arms. Bostrychoceras has a worldwide distribution but is rarely found intact. It typically measures 14cm in height.

This bizarre ammonite is very rare and is only known from Hyogo in Japan. It measures on average 30cm in length. The re-curved hook containing the living chamber is a unique feature and the living animal would probably have drifted in the water column.

Nautilus is the only surviving shelled cephalopod from what clearly was once a vast and diverse family. As the only living representative of the group, many comparative studies have been done on the lifestyle and biology of fossil forms based on the anatomy of Nautilus. Once having a worldwide distribution, today Nautilus is confined to the Pacific Ocean where it maintains a slow and sluggish lifestyle as a predator and scavenger. Although Nautilus is the sole surviving twig on what was once a mighty tree, the story of the shelled cephalopods may not yet be over; the recent discovery of a new genus of Nautilus, Allonautilus, seems to indicate that a new form is currently evolving. What does the future hold?